As of 2 days ago, I have my main desktop running Debian Lenny (currently the testing release, but soon to be stable – more on Debian in a minute).
Read the experience here

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Also, Ive never run Debian as a daily-driver distro. Ive tried if a few times (briefly), but Ive always defaulted back to Ubuntu for that – I always felt it was better suited for the desktop, but Im beginning to change that opinion. Im very happy with the install of Lenny and its running faster than any other distro Ive had on here for an extended period of time. I did do a very customized installation (building up from a base system) and I was very selective about what packages were installed. It seems the Debian release team is shooting for a September release of Lenny, and I plan to stay on Lenny for a while after that, but will probably go to Testing again once its nearing release again.